[Elecraft] K3 Turn on Pop(WAS K3 Audio)

[Paul Christensen]

> Looks like making C8 a little bigger (like 10uF) would help to reduce
> some of the turn on pop that you see on the speakers when powering the
> unit on.  There is mention of this on page 17 under "Selecting External
> Components" > "Bypass Capacitor Value".

A couple thoughts...

First, that may, or may not be the only area contributing to the pop. 
Secondly, the LM4950's click/pop artifact is also a function of the Cin 
value in addition to the Cb value.  National recommends a Cin value no 
larger than 0.39 uF whereas the K3's Cin is 0.47 uF through 20K of series R. 
With the exception of this slight Cin value difference, the K3 uses nearly 
the identical input structure as shown in Figure 2 of the datasheet.  I 
doubt it makes much a difference but experimenting is the only real way to 
know.

>From the datasheet, the only internal workings of the chip are shown with a 
block diagram where Cb controls a bias block.  I would presume that making 
Cb in larger would have the effect of keeping the amp off longer until 
stabilized.  Just a guess though...

In a recent firmware release, I believe the K3's power-on pop was minimized 
although I still hear it on my K3.  Another possibility is to use an 
outboard R/C time-delay relay (set for 1-2 sec), and powered by the rig's 
rear panel aux power connector. That would mimic the manner in which the 
classic '60s and '70s audiophile amplifiers and receivers accomplished the 
pop muting at power-up.  Speaker audio from the K3 would then route to the 
relay contacts before heading off toward the speaker.  Mission accomplished 
and no internal mods to the rig.

Paul, W9AC